<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        new Promise((resolve, reject) => {
            setTimeout(()=> {
                resolve('aaa')
            },1000)
        }).then(res => {
            console.log(res,'，第一层');
            // return new Promise(resolve => {
            //     resolve(res+'111')
            // })
            return Promise.resolve(res+'111')
        }).then(res => {
            console.log(res,',第二层');
            // return new Promise(resolve => {
            //     resolve(res + 'bbb')
            // })
            return res+'bbb'
        }).then(res => {
            console.log(res,',第三层');
        })
    </script>
</body>
</html>